The disclosure concerns a method to control a color printer or color copier in which at least one print marking to control the color printer or color copier is printed on a printing substrate web moving in the movement direction. With the aid of a color measurement sensor unit in a measurement region of this color sensor unit a measurement value of the print marking is determined if the print marking is arranged in the region of the measurement region of the color measurement sensor unit. The controller of the color printer or color copier then takes place depending on this measurement value.
A widespread method to monitor the print quality of a color printer or color copier is, for example, to print markings in the margin region of the printing substrate web in addition to the actual print image, and to detect these with the aid of sensors. Conclusions about the state of the color printer or color copier can be drawn via the information obtained in these measurements. In particular, multiple print markings are applied in the different print colors that are used, wherein the information obtained from them is used for a color regulation (closed loop color monitoring).
For this, the applied print markings for a color sensor unit are detected. This color measurement sensor unit exposes the printing substrate web and calculates a measurement value from the measured reflections integral over a measurement region of the color measurement sensor unit. This measurement value—in particular a color value—is then compared with the preset desired values. The color regulation then takes place depending on the result of this real/desired comparison.
A requirement for a correct color measurement is that—as shown in FIG. 1—the measurement region 12 of the color measurement sensor unit 14 is situated completely on the print marking 16 applied on the printing substrate web 10. In contrast to this, if the measurement region 12 is arranged alongside the print marking 16 (as shown in FIG. 2) or is positioned only partially on the print marking 16 (as depicted in FIG. 3), although the color measurement sensor 14 delivers a measurement value it does not correspond to the actual quality of the print marking 16. Since the unprinted printing substrate is measured as well in this case, at least in part, the integral measurement value determined across the entire measurement region is adulterated. An incorrect color value measurement thus takes place.
Various methods are known in order to avoid such a false measurement. One possibility is to provide an additional optically resolving sensor unit (a camera, for example) in addition to the color measurement sensor unit that is not optically resolving, with the aid of which additional optically resolving sensor unit the position between the color measurement sensor unit and the print marking can be determined. The information obtained in such a manner about the relative position between the color measurement sensor unit and the print marking can then be taken into account in the evaluation of the obtained measurement values.
An additional possibility is that the print markings and the color measurement sensor unit are manually positioned by the operator. The print markings are hereby applied widely such that deviations due to printing substrate web travel fluctuations do not lead to incorrect measurements, and thus do not lead to a malfunction. In this it is disadvantageous that such wide print markings require a great deal of toner or ink and are space-intensive, and limit the effective usable print width.
A method to control a printer is known from the document U.S. Pat. No. 8,107,838 B2, in which print markings are applied to the printing substrate web and a time signal is detected with the aid of a sensor. A maximum value and a minimum value of this sensor signal are determined, based on which a plausibility check of the obtained results is implemented.
The document DE 10 2008 049 908 A1 describes a method to generate a detection signal by means of a detection device to detect a print marking located on a printing substrate web. The detection signal is hereby determined from at least two different color signals.